Melting furnace



Oct. 1, 1968 K. WEBER I 3,404,210

I MELTING FURNACE Filed June 23, 1967 2 Sheets-Sheet 1 FIG I v INVENTOR.

GEORGE K. WEBER BY KAN/(MM ATTORNEY G. K. WEBER MELYT'ING FURNACE Oct.1, 1968 2 Sheets-Sheet Filed'June, 23, 1967 \JW FIG.4

FIG.5

INVENTOR. GEORGE K. WEBER BY M4 ATTORNEY United States Patent 3,404,210MELTING FURNACE George K. Weber, Louisville, Ky., assignor to AmericanAir Filter Company, Inc., Louisville, Ky., a corporation of DelawareFiled June 23, 1967, Ser. No. 648,437 7 Claims. (Cl. 13-22) ABSTRACT OFTHE DISCLOSURE A furnace to melt a thermoplastic material including acrucible defining a chamber in which thermoplastic material is melted,the crucible being provided with heating means so selected segments ofthe outer surface of the crucible can be heated to differenttemperatures to maintain the molten thermoplastic material at differenttemperatures in different portions of the chamber. The crucible furtherincludes a bafiie arrangement to restrict formation of undesirableconvection currents in the molten pool and also includes a multiplicityof orifices to provide means to withdraw the material from the chamberin the form of fine filaments.

Background of the invention Various furnaces have been provided to meltthermoplastic substances, for example glass, so that the material can bedrawn into very fine filaments. One such furnace has included a crucibledefining a chamber to hold glass particles where a flame is directedinto the chamber to melt the particles and form a pool of molten glasswithin the chamber. An orifice plate is provided in the bottom of thecrucible and fine filaments are formed by drawing the molten glassthrough the orifices. Other furnaces have provided a crucible made ofmaterial of selected dielectric characteristics where the crucibledefines a chamber to hold the thermoplastic material for melting and thecrucible is heated by induction heating means. Heat is transferred byconduction from the heated crucible to melt the thermoplastic material.Such induction heating apparatus is expensive, inefiicient, andcomplicated because of the complex control required and because it isgenerally necessary to provide auxiliary cooling means for the inductionheaters.

Furthermore, in drawing glass to form fine filaments the condition ofthe glass at the orifices significantly affects the characteristics ofthe glass filaments so it is desirable to control very closely thetemperature of the molten glass at the orifices. In previous apparatusthe temperature of the molten glass has been measured by temperaturesensing elements located in the pool of molten glass. The heat suppliedto the casing has been controlled in accordance with the temperaturemeasured by the temperature sensing elements but thermal gradients existwithin the molten pool and cause convection currents which make it verydifiicult to accurately determine the temperature and effectivelycontrol the heat provided for the glass.

In some apparatus where molten glass is withdrawn froma melting furnaceto form fine filaments, at least two separate crucibles are provided todefine separated chambers and the glass is maintained at differenttemperatures in the separated chambers. The molten glass is melted inthe first chamber and flows to the second chamber. The second chamberincludes orifice means through which the glass is drawn to formfilaments and is maintained at a selected temperature to provide thedesired properties for drawing filaments. Such an arrangement isexpensive to manufacture and cumbersome to operate.

Patented Oct. 1, 1968 Summary of the invention The present inventionprovides a furnace to melt thermoplastic materials, for example glass,in a crucible where heat is transferred from a radiant heat source toselected segments of the surface of the crucible and the temperature ofthe selected segments of the surface are controlled at differenttemperatures. Furthermore, the present invention advantageously providesa straightforward apparatus including a single melting chamber in whichglass is melted and the molten glass can be maintained at differenttemperatures in different portions of the chamber so it is not necessaryto provide temperature sensitive means Within the chamber to measure thetemperature of the molten glass. Moreover, the present inventionprovides an apparatus to control the condition of molten glass to bewithdrawn from a multiplicity of orifices as filaments without directmeasurement of the temperature of the molten glass.

Various other features of the present invention will become obvious tothose skilled in the art upon reading the disclosure set forthhereinafter.

More particularly, the present invention comprises: a crucible defininga melting chamber having a multiplicity of orifices so material meltedwithin the chamber is emitted through the orifices to form filaments;crucible heating means including first radiant heat source disposed todirect heat to a first segment of the outer surface of the crucible anda second radiant heat source disposed to direct heat to a second segmentof the outer surface of the crucible between the first segment and theorifice means; control means to regulate the first heat source tocontrol the temperature of the surface of the first segment of thecrucible within selected limits and regulate the second heat source tocontrol the temperature of the surface of the second segment of thecrucible within selected limits; and, baffle means included within thechamber and disposed adjacent the orifice means to direct the flow ofmolten thermoplastic material toward the walls of the crucible andrestrict convection currents within the molten material.

It is to be understood that the description of the present inventiongiven herein is not by way of limitation and that various changes can bemade in the arrangement, form, or configuration of the apparatusdisclosed herein without departing from the scope or spirit of thepresent invention.

Referring now to the figures:

FIGURE 1 is an elevational view, in section, of an apparatus inaccordance with the present invention;

FIGURE 2 is a view taken along a plane passing through line 2-2 ofFIGURE 1;

FIGURE 3 is an enlarged view of an orifice plate which can be used in anapparatus in accordance with the present invention;

FIGURE 4 is a view taken along a plane passing through line 44 of FIGURE3;

FIGURE 5 is a perspective view of a cover plate and baffle arrangementwhich can be used in an apparatus in accordance with the presentinvention; and

FIGURE 6 is a perspective, partially broken away, view of a heaterelement which can be used in an apparatus in accordance with the presentinvention.

The apparatus of the example of the figures can be used to melt :aselected thermoplastic material, for example glass, where the moltenmaterial is emitted from the apparatus as fine filaments.

The apparatus of the example includes an open end cylindrical crucible 1which can, advantageously, be made of a thermal conductive heatresistant material for example Inconel, to contain in chamber 2 definedthereby molten glass at very high temperature and can be of uniformdiameter to provide a continuous pool of molten material. One end ofchamber 2 of crucible 1 is bounded by a plate 9 which includes anorifice plate 3 having a multiplicity of orifices for emission of glassfrom chamber 2 in the form of very fine filaments. Crucible 1 iscontained within an outer casing 11.

In the example shown in FIGURE 1, crucible 1 is partially encased byheating elements 6 which are provided to heat selected portions of thesurface of crucible 1. Each heating element 6 can include a cylindricalinsulator 17 which can be made of heat insulating material, for examplemolded ceramic, and a resistance heating coil 5. In the example ofFIGURE 1 three heating elements 6a, 6b, and 6c are provided to heatdifferent segments of the surface of crucible 1.

Referring to FIGURE 6, insulator 17 of each heating element 6 can becylindrical and can include inwardly directed peripheral flanges 17a atopposite ends to define a recess therebetween which is adapted toreceive the aforementioned radiant heat emitting resistance coils 5.Flanges 17a likewise define an aperture to receive crucible 1 so thatwhen the apparatus is assembled as shown, elements 6 surround crucible 1in stacked relation. The area of the surface of crucible 1 to be heatedby each heating element -6 is a cylindrical segment defined betweenflanges 17a of each heating element 6.

The inner surface of the insulator of each heating element 6 can belined with a reflective material 15, as shown, so radiation emitted fromcoils 5 is reflected toward crucible 1 and the heat is not lost but isabsorbed by crucible 1. Advantageously, coils 5 can be disposed withinthe recesses in insulator 17 of each element 6 to avoid contact withboth crucible 1 and reflector surface so there is no conductive heattransfer from coils 5 to crucible 1 and no electrical short circuitbetween coils 5 and lines 15.

An electric power supply 10 is provided to furnish power for coils 5 andincludes sepanate power sources 10a, 10b, 100 for each of the resistancecoils 5a, 5b, 5c, respectively, so the heating elements can beindependently and selectively operated.

In accordance with one feature of the present invention temperaturesensitive elements 8a, 8b, 8c are provided to measure the temperature ofthe segment of the surface of crucible 1 heated by the respectiveheating elements 6a, 6b, and 60. Each temperature sensitive element, forexample a thermocouple, transmits the temperature at the particularsegment of the surface of crucible 1 to power supply 10 to control theflow of electric current to the individual resistance heating coil 5 andmaintain the segment of the surface of crucible 1 at the desiredtemperature.

In the example of the figures glass melted in chamber 2 is emitted fromcrucible 1 through orifices 21 of orifice plates 3. Referring to FIGURE3, orifice plates 3 are of semi-circular configuration and of corrugatedcross-section with a multiplicity of orifices 21 of selected diameterprovided at the crest of each of the corrugations. A cover plate 19 isprovided to be received by one end of crucible 1 and includessemi-circular slits adapted to receive orifice plates 3 (FIGURES 21and 5which are disposed in cover plate 19 in an annular configuration. Plate19 includes a flange 9 defining a surface 90 to contact crucible 1, asshown in FIGURE 1. In the example of the figures a bafile 4 extendsupwardly from the central portion of cover plate 19 into chamber 2 todefine an annular chamber 2a between baffle 4 and casing 1 adjacentorifice plates 3.

As shown in FIGURE 1, crucible 1, heating elements 6, and end plate 19can be assembled in a cylindrical casing 11. Casing 11 can be split, asshown in FIGURE 2, to facilitate assembly and can be made of heatinsulating material, for example molded ceramic. Casing 11 includes arecessed portion, as shown, to receive heating elements 6 and flaredlltlet 18 having a diameter greater than the diameter of annular orificeplates 3. Filaments emitted from orifices 21 are drawn through outlet 18to be wound on a selected collector, not shown. A lip 9a is provided incasing 11 to receive flange 9 of plate 19 and crucible 1 rests onsurface 9c of flange 9 as hereinbefore described.

In some apparatus in accordance with the present invention it isdesirable to distribute the solid thermoplastic material toward thewalls. For example, a spider support 14 can be provided to be supportedby casing 11 and disposed adjacent opening 7 of crucible 1 to mount adistributor 12. Spider 14 can include a central threaded element 16 anddistributor 12 can include a threaded shank 13 adapted to be received byelement 16 so that distributor 12 can be raised and lowered withinchamber 2 by turning shank 13.

When the furnace of FIGURE 1 is used to melt glass, large particles ofglass can be introduced through opening 7 and are deflected toward theheated walls of easing 1 by distributor 12.

In the example of the figures, three cylindrical segments of the surfaceof crucible 1 are defined by and receive heat from, three heatingelements 6a, 6b, and 6c as hereinbefore described. The heaters areindividually controlled in accordance with the surface temperature ofcrucible 1 in the area heated by the respective heating elements so thatthe different cylindrical segments can be maintained at differenttemperatures. Heat transmitted from heaing coils 5 to crucible 1 isconducted to the glass within the chamber and the temperature of theglass approaches the temperature of the crucible.

In the example of the figures, most of the glass particles are melted inthe portion of chamber 2 defined by the segment of crucible 1 heated byelement 6a and that segment of crucible 1 is maintained at a highertemperature than the segments of the crucible heated by elements 6b and60 which define portions of chamber 2 where the glass is in a moltenstate.

Advantageously, element 6c can maintain the surface of crucible 1 at atemperature below the temperature of the surface heated by element 6aand slightly above the desired temperature of the glass within theannular chamber 2a so the glass is heated to the desired temperatureimmediately before emission from crucible 1 to provide the propercharacteristics in the glass to be drawn as filaments from orifices 21.

The segment of surface of crucible 1 heated by element 6b can bemaintained at a temperature lower than the temperature of the segmentheated by element 60, but high enough to assure the glass remains in amolten state in chamber 2, so the molten glass is cooled to atemperature below the desired temperature for drawing filaments but highenough to assure the glass is in a molten state.

Thus, glass is melted in the portion of chamber 2 heated by element 6a.The temperature of the molten pool can then be reduced but the meltingprocess is completed in the portion of chamber 2 heated by element 6b.Finally, the molten pool can be reheated by element 60 to provide thedesired temperature for drawing filaments and it is not necessary toprovide direct measurements of the temperature of the glass in chamber2.

Because of the thermal gradients which purposely exist Within chamber 2convection currents would normally occur and would adversely affect thetemperature and characteristics of the glass drawn from the chamber 2a.The currents would be particularly severe in chamber 2a where the glassis reheated. To prevent such convection currents the present inventionprovides baflie 4 to restrict flow of convection currents in the portionof crucible 1 heated by element 6c to assure uniform, controlled glasstemperature in annular chamber 2a and the characteristics andtemperature of the molten glass emitted from orifice plate 3 can be verycarefully controlled without directly measuring the temperature of theglass within casing 1.

The invention claimed is:

1. A furnace to melt a thermoplastic material comprising: a crucibledefining a melting chamber in which the thermoplastic material ismelted, said crucible including a multiplicity of orifices so materialmelted within said chamber is emitted through said orifices to formfilaments; radiant heat means including a first radiant heat source todirect heat to a first selected segment of the surface of said crucibleand a second radiant heat source disposed to direct heat to a secondselected segment of the surface of said crucible where said secondsegment of said surface is between said first segment and said orificemeans; control means to regulate said first radiant heat source tocontrol the temperature of said first segment of said crucible withinselected limits and regulate said second radiant heat source to controlthe temperature of said second segment of said crucible within selectedlimits; and, bafile means disposed within said chamber adjacent saidorifice means to restrict convection currents within said pool of moltenmaterial in the area of said chamber adjacent said orifice means.

2. The apparatus of claim 1 including a third radiant heat source meansdisposed to direct heat toward a third segment of the surface of saidcrucible between said second segment and said orifice means and controlmeans to regulate said third radiant heat source means to control thetemperature of said third segment of said crucible within selectedlimits.

3. The apparatus of claim 1 wherein said orifice means includes anorifice plate having a multiplicity of orifices in an annulararrangement with bafile means disposed to extend into said chamber fromthe central portion defined by said orifice means.

4. A furnace to melt a thermoplastic material comprising: a cylindricalcrucible defining a melting chamber to melt a thermoplastic material;orifice Plate means adjacent one end of said cylindrical crucible, saidorifice means having a multiplicity of orifices so material meltedwithin said chamber is emitted through said orifices to form filaments;crucible heating means including first radiant heat element disposed todirect heat toward a first cylindrical segment of the surface of saidcrucible, second radiant heat element disposed between said first heatsource means and said orifice means to direct radiant heat toward asecond cylindrical segment of the surface of said crucible between saidfirst segment and said orifice means, and third radiant heat element todirect heat toward a third cylindrical segment of said crucible betweensaid second segment and said orifice means; control means to control thesupply of power to said first heat element including means to controlthe temperature of said first segment of said crucible within firstselected limits, to regulate said second radiant heat element to controlthe temperature of the surface of said second segment of said cruciblewithin a second selected range of temperature lower than said firsttemperature range and regulate said third heat element to control thetemperaure of the surface of said third segment of said crucible withina selected temperature range between said first and second temperatureranges; and, bafile means extending from said orifice plate means intosaid chamber defined by said crucible means to direct the flow of moltenthermoplastic material toward the walls of said crucible and restrictconvection currents within said molten material in the portion of saidchamber adjacent said orifice means.

5. The apparatus of claim 4 wherein said crucible is of uniformdiameter.

6. The apparatus of claim 4 wherein said radiant heat elements comprise:cylindrical casing means to hold a radiant heat source to direct to saidcrucible wherein the internal diameter of said casing is greater thanthe diameter of said crucible so said element defines a cylindricalsegment of the surface of said crucible to be heated by said heaterelement.

7. The apparatus of claim 4 wherein said orifice means are arranged inan annular configuration in said orifice plate and said baflle extends,from the central portion of i said orifice plate defined by said orificemeans, into said chamber to define an annular chamber between saidbafile means and the inner surface of said crucible.

References Cited UNITED STATES PATENTS 1,933,851 11/1933 Granzer 219424XR 2,767,300 10/1956 De Verter 219-421 2,924,695 2/1960 Atkeson 219-352XR 2,963,529 12/1960 Schmidt 219-422 XR 3,187,076 6/1965 M-achlan et al13-6 FOREIGN PATENTS 642,858 9/ 1950 Great Britain.

BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

